1. Field of the Invention
The invention relates to a capillary electrophoresis apparatus which separates and analyzes samples such as DNA and protein by electrophoresis, particularly to an autosampler (apparatus for automatically transporting sample containers) which transports containers holding a solution.
2. Description of the Related Art
With reference to the capillary electrophoresis apparatus, a component of a sample is separated by introducing the sample into a capillary filled with separation media and applying a high voltage to both ends of the capillary. Sample plates holding samples have various forms. Generally, the sample plate having 96 wells (arranged in an 8×12 matrix with a pitch of 9 mm) and the sample plate having 384 wells (arranged in a 16×24 matrix with a pitch of 4.5 mm) are used.
An example of a sample plate assembly is described in Japanese Patent Application Laid-Open Publication No. 2001-324474 (JP-A-2001-324474). The sample plate assembly has a structure in which the sample plate on which a septer having a function of preventing evaporation of the samples is mounted is sandwiched between an upper-side septer holder and a lower-side adapter.
A mechanism in which the sample plate assembly is held by a gripper is disclosed in Japanese Patent Application Laid-Open Publication No. 2003-344357 (JP-A-2003-344357). The gripper holds the sample plate assembly directly, thereby allowing the sample plate assembly to be held.
Recently, there has been a demand for improvement in operability and measuring speed of the capillary electrophoresis apparatus. In order to satisfy the demand, it is necessary to simplify operation for disposing the sample plate assembly on a moving stage of the autosampler.
The autosampler transports each container which contains solutions such as a sample solution, buffer solution, assy solution, cleaning liquid, and waste liquid to a capillary anode electrode. The capillary anode electrode is formed on a capillary electrode. The capillary electrode has a structure in which the end of the capillary is integrated with an electrode for electrophoresis. The capillary electrode is fixed on a load header. On the other hand, each container is disposed on the moving stage of the autosampler and is movable in the direction of three dimensions of X-Y-Z. Each container is first transported to under the capillary anode electrode by the autosampler and then moved upward. As a result, contact of the capillary electrode with the solution is realized.
When the sample plate is transported by the autosampler, a type of sample plate needs to be recognized. Therefore, a sample plate identification mechanism for identifying the type of sample plate is provided in the autosampler. In the sample plate identification mechanism described in JP-A-2001-324474, a detection plate is provided on the bottom surface of the adapter and a photo interrupter is provided on the upper surface of the moving stage of the autosampler. When the sample plate assembly is disposed on the moving stage, the photo interrupter is engaged with the detection plate. The light from the photo interrupter is blocked by the detection plate. As a result, the type of sample plate can be detected. A type of identifiable sample plate can be increased by increasing the numbers of the photo interrupters and the detection plates.
The sample plate identification mechanism using both the photo interrupter and the detection plate has an advantage that the type of sample plate can always be identified while the sample plate assembly is disposed on the moving stage. For example, the type of sample plate is analyzed by a sample processing program and then the analyzed result can be presented to an operator. When the type of sample plate cannot be analyzed by the sample processing program, wrong measurements can be prevented by stopping the operation of the autosampler.
However, the photo interrupter is exposed on the moving stage in the sample plate identification mechanism using both the photo interrupter and the detection plate. In the capillary electrophoresis apparatus, the operator places containers containing liquids such as a buffer solution, cleaning liquid, and waste liquid on the moving stage. For that reason, liquids may fall on the photo interrupter due to the operator's carelessness. Further, a cable for supplying an electric power and transmitting a signal is connected with the photo interrupter. The cable moves together with the moving stage whenever the moving stage moves.
As described above, there is a demand for improvement in operability and measuring speed of the capillary electrophoresis apparatus. In order to satisfy the demand, the development of the sample plate identification mechanism in which it is not necessary to form the photo interrupter on the moving stage has been required.